Automatic injection devices

ABSTRACT

An injection device comprises a syringe extendible against a spring bias from a retracted position in a housing to a projecting injecting position. A spring biased plunger has collapsible elbows which, when the plunger is released, initially engage the end of the syringe to drive it to the projecting position, whereupon arresting of the syringe movement causes the elbows to collapse inside the syringe to allow the plunger to engage and drive the bung.

BACKGROUND

There are various forms of automatic injection device which when operated cause the needle of a syringe to be moved forwardly so that it projects from a protective housing prior to actuation of the syringe to express a dose of liquid through the needle. It is important to try to ensure that the syringe is moved bodily forward to expose the needle before the liquid charge is pressurised so that dribbling from the needle does not occur before the actual injection takes place. It is an object of this invention to provide a mechanism which operates in this desired manner.

SUMMARY

According to the invention there is provided an injection device for causing a dose of liquid to be ejected from the needle at one end of a syringe located within a housing of the device, the syringe being movable by a plunger, upon release of an actuating bias member at one end of the housing, to move the syringe, from a first position wherein the needle is shrouded by the housing, to a second position wherein the needle projects from the other end of the housing, the plunger being in the form of a rod with a longitudinally centrally located flexible projecting portion which, prior to release of said actuating bias member, is situated beyond the other end of the syringe, such that a primary movement of the plunger, under the bias of the actuating bias member, will cause the projecting portion to bear against the other end of the syringe such that the syringe is moved from said first to said second position, whereupon arresting of further movement of the syringe, results in the flexible portion collapsing inwardly so that it enters the syringe, thus enabling the plunger to move by a secondary movement, within the syringe, into contact with and to act upon a plug to compress the liquid within the syringe and cause expression of the liquid through the syringe needle.

With such an arrangement, the projecting portion will remain in its projecting position (in order to move the syringe from the first to the second position) until the force increases to such an extent which allows the projecting portion to collapse inwardly so that the plunger can then move within the syringe to cause the liquid to be expressed through the syringe.

The projecting portion can comprise one or more flexible elbows projecting beyond the normal circumference of the rod, but compressible into said circumference. This could be in the form of two elbows defined either side of a longitudinal slit in the rod. The elbows could be pre-formed as a pair of arms either side of the longitudinal slit between upper and lower solid portions of the rod.

Preferably the injection device will contain a return bias member acting between the syringe housing and the other end of the syringe to hold the syringe retracted within the housing until the actuating bias member is released. One or more of the bias members provided within the housing can be in the form of a coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be performed in various ways and a preferred example thereof will now be described, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a sectional view through an injection device of this invention prior to use; and

FIGS. 2 and 3 are similar views showing successive stages of operation of the injection member.

DESCRIPTION

The injection device shown in the drawings comprises a syringe 1 located within a protective housing 2. The syringe comprises a 3 incorporating a liquid dose held in place by a bung 4 and having a needle 5 through which the dose can be ejected by applying pressure to the bung 4. The 3 has an enlarged head 6. A plunger 7 is biased forwardly by a coil spring 8, but is held back in a latched position (FIG. 1) until such time as a trigger shown schematically at 11 is actuated to release the plunger and the spring 8. Prior to use the syringe 1 is held retracted in the housing 2 by a coil spring 9.

It will be seen that the plunger 7 is in the form of a rod having a central portion which defines a pair of projecting elbows 10. These can be pre-formed as part of a moulded plunger 7. The projecting elbow portions 10 are flexible so that they can be moved inwardly to cause that portion of the rod to adopt a circumference similar to that of the rest of the rod. As can be seen in FIG. 2, when the plunger is released and biased by the spring 8 the expanded region formed by the elbows 10 rests against the head 6 of the 3 and the force provided is sufficient to compress the spring 9 until such time as the head 6 abuts the top of the housing 2, whereupon further movement of the 3 is arrested. The continual bias created by the spring 8 then causes the elbows 10 to be 20 compressed inwardly as they enter into the interior of the 3. With the elbows 10 in the collapsed state, the plunger can then move relatively easily within the 3 so as to act upon the bung 4 and thus cause the contents of the syringe to be ejected through the needle 5.

The illustrated configuration of the plunger 7 provides several technical advantages. It can be moulded integrally. Also the collapsing movement of the projecting elbows provides an arrangement which can provide a suitable injection force to cause the needle to enter the skin to a suitable depth, but then provide a relatively low drag against the inner wall of the syringe container so that the major portion of the thrust of the spring for the remainder of its stroke is applied to the bung 4. It will be appreciated that other configurations of collapsing projection could be used in place of the collapsing elbows. 

1-7. (canceled)
 8. An injection device, comprising: a housing; a syringe coupled to a needle at one end, the syringe slideably mounted within the housing for movement between a first position relative to the housing in which the needle is shrouded by the housing and a second position relative to the housing in which the needle projects from the housing; a bung slideably mounted in the syringe and moveable to expel a liquid through the needle; a plunger comprising: an upper solid portion, a lower solid portion having one end operable to move the bung and to transmit an expulsion force thereto, and a projecting region comprising one or more flexible elbows on either side of a central void provided between the upper and lower solid portions of the plunger, the plunger having a first length when the projecting region is in a projecting position in which the one or more elbows project outwardly from the central void, the plunger having a second length greater than the first length when the projecting region is in a collapsed position in which the one or more elbows are collapsed inwardly toward the central void; and an actuating bias member provided at one end of the housing and operable to move the plunger toward another end of the housing.
 9. The injection device as claimed in claim 8, wherein the projecting region of the plunger is configured to drive the syringe from the first position relative to the housing to the second position relative to the housing such that the needle projects from the housing.
 10. The injection device as claimed in claim 8, wherein the projecting region of the plunger is in the projecting position prior to entering the syringe and wherein the projecting region is in the collapsed position inside the syringe for applying the expulsion force to the bung in order to compress the liquid in the syringe and cause expression of the liquid from the syringe, wherein a collapsing movement of the projecting region toward the central void from the projecting position outside the syringe to the collapsed position inside the syringe causes elongation in the length of the plunger from the first length to the second length.
 11. The injection device as claimed in claim 8, wherein the central void is a longitudinally extending slit.
 12. The injection device as claimed in claim 8, further comprising: a return bias member acting between the housing and another end of the syringe to hold the syringe in the first position relative to the housing until the actuating bias member is released.
 13. The injection device as claimed in claim 8, wherein one or more of the bias members provided within the housing is in the form of a coil spring.
 14. The injection device as claimed in claim 8, wherein the housing is fixed relative to the syringe.
 15. The injection device as claimed in claim 8, wherein the plunger is molded integrally.
 16. A syringe assembly, comprising: a syringe coupled to a needle at one end, the syringe slideably mounted within a housing for movement between a first position relative to the housing in which the needle is shrouded by the housing and a second position relative to the housing in which the needle projects from the housing; a bung slideably mounted in the syringe; and a plunger comprising: an upper solid portion, a lower solid portion having one end operable to move the bung and to transmit an expulsion force thereto, and a projecting region comprising one or more flexible elbows on either side of a central void provided between the upper and lower solid portions of the plunger, the plunger having a first length when the projecting region is in a projecting position in which the one or more elbows project outwardly from the central void, the plunger having a second length greater than the first length when the projecting region is in a collapsed position in which the one or more elbows are collapsed inwardly toward the central void.
 17. The syringe assembly as claimed in claim 16, wherein the projecting region of the plunger is configured to drive the syringe from the first position relative to the housing to the second position relative to the housing such that the needle projects from the housing.
 18. The syringe assembly as claimed in claim 16, wherein the projecting region of the plunger is in the projecting position prior to entering the syringe and wherein the projecting region is in the collapsed position inside the syringe for applying the expulsion force to the bung, wherein a collapsing movement of the projecting region toward the central void from the projecting position outside the syringe to the collapsed position inside the syringe causes elongation in the length of the plunger from the first length to the second length.
 19. The syringe assembly as claimed in claim 16, wherein the central void is a longitudinally extending slit.
 20. The syringe assembly as claimed in claim 16, wherein the housing is fixed relative to the syringe.
 21. The syringe assembly as claimed in claim 16, wherein the plunger is molded integrally.
 22. A method for operating an automatic injection device, the method comprising: operating an actuating bias member to move a plunger including a projecting region comprising an upper solid portion, a lower solid portion and one or more flexible elbows on either side of a central void provided between the upper and lower solid portions of the plunger, wherein the projecting region is in a projecting position when the one or more elbows project outwardly from the central void and in a collapsed position when the one or more elbows are collapsed inwardly toward the central void; and engaging one end of a syringe with the plunger to drive the syringe from a first position relative to a housing in which a needle coupled to another end of the syringe is shrouded by the housing to a second position relative to the housing in which the needle projects from the housing; wherein the projecting region of the plunger is in the projecting position prior to entering the syringe and wherein the projecting region is in the collapsed position inside the syringe for applying an expulsion force to a bung in the syringe in order to compress a liquid dose in the syringe and cause expression of the liquid dose from the syringe, wherein a collapsing movement of the projecting region toward the central void from the projecting position outside the syringe to the collapsed position inside the syringe causes an elongation in the length of the plunger.
 23. The method as claimed in claim 22, wherein the central void is a longitudinally extending slit.
 24. The method as claimed in claim 22, further comprising: holding the syringe in the first position relative to the housing using a return bias member acting between the housing and another end of the syringe, until the actuating bias member is released.
 25. The method as claimed in claim 22, wherein the housing is fixed relative to the syringe.
 26. The method as claimed in claim 22, wherein the plunger is molded integrally. 